1. Field of the Invention
The present invention relates to a surface treatment method. More specifically, the present invention relates to a surface treatment method for a contact portion of a diaphragm spring and a plate member that slides there-against.
2. Background Information
Clutches are designed to transfer and interrupt torque from an engine to a transmission in a vehicle or the like. Conventionally, clutches are equipped with a clutch cover assembly for pressing and releasing a clutch disk against and from a flywheel. The clutch cover assembly chiefly has a pressure plate, a diaphragm spring or coil spring, and a clutch cover. The pressure plate pinch-holds the clutch disk between itself and the flywheel. The diaphragm spring or coil spring presses the pressure plate against the clutch disk. The clutch cover is fixed to the flywheel and supports the spring and pressure plate.
A conventional diaphragm spring used in a diaphragm spring type clutch cover assembly has a ring-shaped elastic part and a plurality of lever parts that extends radially inward from the elastic part. A release bearing or other release member touches against the contact portion of the tips of the levers of the diaphragm spring through the plate member. The pressure exerted on the pressure plate by the diaphragm spring is applied and removedxe2x80x94and the clutch is engaged and disengagedxe2x80x94in accordance with the axial movement of the release member. Thus, the tip sections of the levers of the diaphragm spring are a contact portion that is moved by the release member through the plate member. The tip sections slide on the plate member each time the clutch is engaged and disengaged. Therefore, measures against wear are conventionally taken with respect to the sliding portions. For example, in addition to induction hardening, the metal surfaces of the sliding portions are plated with hard chrome or thermal-sprayed with a molybdenum coating. The adhesion between the hard chrome plating and the base material is not particularly high. Thus, the plating cracks and exfoliates when large loads act thereon. Furthermore, the chrome plating process generates chromium VI, which is considered to be environmentally unfriendly. When molybdenum thermal spraying is used, insufficient adhesion results from the existence of porosity and, consequently, sufficient wear resistance cannot be obtained.
In view of the above, there exists a need for a surface treatment method for a contact portion of a diaphragm spring and a plate member that slides there-against that overcomes the above-mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
An object of the present invention is to provide a surface treatment method that increases the wear resistance of the tip sections or contact portions of the levers of the diaphragm spring in a clutch cover assembly and of the plate member that slides there-against.
A surface treatment method in accordance with a first aspect of the present invention is a surface treatment method for a contact portion of a diaphragm spring in a clutch cover assembly and/or a plate member that slides there-against. In this method, the contact portion of the diaphragm spring and/or the sliding portion of the plate member are/is designated as a treatment surface. The treatment surface is subjected to an electric discharge coating treatment using a coating material such that the treatment surface is covered with a coating layer of approximately 50 xcexcm or less and a diffusion layer is formed inside the treatment surface.
In contrast to conventional methods, this method is not limited to forming a coating layer on the plate member and the contact portion of the diaphragm spring. This method also forms a diffusion layer, or a layer formed by the coating material diffusing/penetrating into of the treatment surface, inside the treatment surface by means of electric discharge coating. Thus, the adhesion between the coating layer and the base material is improved. In other words, the adhesion between the coating layer and the contact portion of the diaphragm spring or the sliding portion of the plate member is improved. As a result, the wear resistance is improved. Additionally, since the thickness of the coating layer covering the treatment surface is approximately 50 xcexcm or less, the formation of unnecessary coating is suppressed while obtaining sufficient wear resistance to satisfy the service life of the clutch.
A surface treatment method in accordance with a second aspect of the present invention is a surface treatment method according to the first aspect, wherein the treatment surface is covered with a coating layer of approximately 10 to 50 xcexcm.
A surface treatment method in accordance with a third aspect of the present invention is a surface treatment method according to the first or second aspect, wherein the treatment surface is covered with a coating layer having an average thickness of 20 to 40 xcexcm.
A surface treatment method in accordance with a fourth aspect of the present invention is a surface treatment method as recited in any of the first to third aspects, wherein the coating material is molybdenum, tungsten carbide, titanium carbide, chromium carbide, or titanium boride.
These and other objects, features, aspects, and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.